The present invention relates to a method for regulating or controlling the charge state of an electrical energy accumulator of a hybrid vehicle.
It is known that hybrid vehicles distinguish themselves by the combination of an internal-combustion engine and at least one electric machine. In the case of a so-called “full hybrid”, the vehicle can optionally be driven by only the internal-combustion engine, by only the electric motor, or by the internal-combustion engine assisted by the electric motor. In the case of a so-called “mild hybrid”, the electric machine is provided only for assisting the internal-combustion engine as well as for recuperating kinetic energy of the vehicle during coasting phases. Purely electric driving is not possible in the case of a mild hybrid.
Some hybrid concepts also have a so-called engine start/stop function. When the vehicle is stationary, for example, in a traffic jam or in front of a red traffic light, the automatic start/stop system will automatically switch off the internal-combustion engine. If a large amount of electric power is withdrawn from the battery, when the vehicle is stationary, for example, by an electrically driven compressor of the vehicle air-conditioning system, this could lead to a rapid lowering of the charge state of the battery. In order to prevent the charge state from falling into a critical range, in which there would be the risk that certain vehicle functions may fail, the battery has to be charged in time by use of the internal-combustion engine; i.e., when the vehicle is stationary, the internal-combustion engine has to be started additionally, if required; or, when the internal-combustion engine is already running, the load point has to be raised correspondingly. For conventional hybrid concepts, it is provided in this case that the battery is charged to a certain, precisely predefined upper charge state value.
If the charge state to which the energy accumulator is charged by way of the internal-combustion engine is selected to be too low, this may result in a frequent switching-on and off of the internal-combustion engine when the electrical system load is high. If, in contrast, the charge state to which the energy accumulator is charged by way of the internal-combustion engine is selected to be relatively high, it may take a very long time before the battery is charged to the corresponding level and the internal-combustion engine can be switched off again, which is undesirable particularly in traffic jam phases in which traffic comes to frequent standstills and the driver would not expect an automatic switching-off of the internal-combustion engine.
It is an object of the invention to provide a method for controlling or regulating the charge state of an electrical energy accumulator of a hybrid vehicle, where the charging of the energy accumulator takes place as much as possible according to the requirements.
This and other objects are achieved by a method for controlling or regulating the charge state of an electrical energy accumulator of a hybrid vehicle, where, in some operating states, the energy accumulator is charged from a low to a higher charge state level by way of an electric machine driven by an internal-combustion engine of the hybrid vehicle and operating as a generator. The level of the charge state to which the energy accumulator is charged by way of the internal-combustion engine is selected as a function of a parameter representing the load of the electrical system or correlating thereto.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.